In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.
For example, the use of Multi-Operator Radio Access Networks (MORANs), also known as Radio Access Network (RAN) sharing, and Multiple Operator Core Network (MOCN) are ways for multiple mobile telephone network operators to share radio access network infrastructure. The same network infrastructure may thus be used to transmit/receive for different operators. A management information base (MIB) may contain a list of multiple public land mobile network (PLMN) Identities. The wireless device (or user equipment, UE) may read the MIB and select a PLMN to register to, based on its subscription. A wireless device that does not support network sharing in the sense that it ignores the additional broadcast system information that is specific for network sharing is denoted a non-supporting wireless device or a network sharing non-supporting UE. A wireless device that supports network sharing in the sense that it is able to select a core network operator as the serving operator within a shared network is denoted a supporting wireless device or a network sharing supporting UE.
One task in a MOCN network is the selection of a serving core network (CN) operator. In a Long Term Evolution (LTE) network, this simply means that a serving operator needs to be selected for the UE in the packet switched (PS) domain. In the Global System for Mobile Communications (GSM) and in Wideband Code Division Multiple Access (WCDMA) networks, however, it needs to be ensured that the same serving operator is selected for the UE in both the circuit switched (CS) domain and the PS domain, thus resulting in so-called CS/PS coordination.
For a wireless device in idle mode, mobility selection of the serving CN operator is done either directly or indirectly. The mobility selection of the serving CN operator is done directly by the UE if the UE is a supporting UE and if the RAN and the CN also supports supporting UEs. The mobility selection of the serving CN operator is done indirectly by using the MOCN redirection function in the RAN and CN if the UE is a non-supporting UE or if the RAN and the CN does not support supporting UEs.
The current release of the 3rd Generation Partnership Project (3GPP) standard (TS 23.251 v12.1.0) does however not guarantee, for all mobility scenarios, that the same operator is selected in both the CS and the PS domains. For that reason a work has been initiated in 3GPP (see WID SP-140168 Improvements to CS/PS coordination in UTRAN/GERAN Shared Networks) with the following justification where it is noted that there is support of Network Sharing in UTRAN/GERAN specifications where radio access and core network can be shared between operators without this being known to the UEs. One challenge in the context of this functionality is to ensure that the registration of a given UE to the CS and PS domain is coordinated, i.e. a subscriber is registered to the same PLMN in both domains. UTRAN is short for Universal Terrestrial Radio Access Network and GERAN is short for GSM EDGE RAN, where EDGE is short for Enhanced Data Rates for GSM Evolution. It is in WID SP-140168 Improvements to CS/PS coordination in UTRAN/GERAN Shared Networks further noted that initial analysis has shown that there are issues with CS/PS coordination in least in the case of network-controlled mobility into UTRAN/GERAN shared networks i.e. CS/PS coordination failure resulting in UE ending up registered to different operators in the CS and PS domains.
Recently this has resulted in a 3GPP TR 23.704 v 1.1.0 and within that an agreement to base the normative CRs upon solution #5; see Chapter 8, Conclusion where it is stated that it is concluded based on evaluation of solutions in section 7 that solution #5 is selected as the basis for further normative work. Further work will occur via normative CRs and there will be no further additions, alignments or corrections to the technical report.
Solution #5 (see Chapter 7.5 in TR 23.704) includes among other things a procedure in which CS/PS coordination for some scenarios is performed by the RAN node based on data (old location area identity (LAI) or routing area identification (RAI), CS/PS-network resource indication (NRI) and indication if UE is attaching) provided by the CN node in both the CS and the PS domain. By use of this data it is possible to conclude whether the UE is roaming within an operator coordinated area and thus can be regarded as CS/PS coordinated. When serving operator is selected based on the operator coordinated area this must be applied for both CS and PS domain.
The above described procedure will work properly when all network nodes (such as base station controller BSC, radio network controller RNC, serving GPRS support node SGSN, and mobile switching centre MSC) are upgraded and thereby capable of providing data (the SGSN and the MSC) or capable of acting upon the provided data (the BSC or the RNC). However as stated above the concept of operator coordinated area must be applied in both the CS and PS domain or not at all. And since registration in the PS domain (for routing area update, RAU) and in the CS domain (for location area update, LAU) is not always concurrent it is not possible to check the support level during a registration procedure. For example if the RAN node and the SGSN node supports the new procedure whilst the MSC does not and RAU occur first, then it will not be ok to apply the new procedure for the PS domain as it will not be possible to apply it for the CS domain.
For other scenarios CS/PS coordination is performed by the RAN node based on queries sent to the CN nodes in the CS and the PS domain. Similarly this must be supported in both the CS and the PS domain or not at all.
Hence, there is still a need for an improved provision of support capability in communications networks.